He was practicing a fast draw. Cocking the hammer is part of a fast draw with a single action revolver.
However, he should have lowered the hammer down on the chamber, not pointed it at someone and pulled the trigger.
He aimed at her and blasted her in the chest at near point blank range.
I just saw THE GODLESS on Netflix. There were hundreds and hundreds of bullets flying all over the place in that movie. It looked real, yet no one was hurt.